Motor-type ink sensor

Abstract: A motor-type ink sensor for detecting ink in a printing means of a printing apparatus (1), comprising an agitating part (22) disposed in a position of an ink fountain (50) formed in the printing means, a motor (21) for driving to rotate the agitating part (22), and a control section (24) for detecting ink from the driving condition of the motor (21).

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ink detecting device useful for a printing apparatus such as a mimeograph apparatus and so forth, and more particularly to a motor-type ink sensor for detecting the presence or absence of ink by the driving condition of a motor which drives to rotate an agitating part in ink. 2. Description of the Related Art As a means for detecting ink in a printing apparatus and so forth, an electrical capacitance ink detecting device as shown in Fig. 12 is described in Japanese unexamined patent application 558-62520. In this ink detecting device, a ink roller and a squeegee roller and an ink detecting electrode which contacts an ink fountain defined therebetween serve as counter electrodes to constitute a capacitor. This capacitor and a coil not illustrated form an oscillatory circuit. The oscillation frequency of the oscillatory circuit is determined by the capacity of the capacitor when coil inductance is fixed. And the electrostatic capacity of the capacitor is determined by the quantity of ink. Therefore, the quantity of ink supplied between these rollers corresponds to the oscillation frequency of the oscillatory circuit, and the quantity of ink can be detected by use of this oscillation frequency. According to the ink detecting device of electrostatic capacity type described above, it is imperative to accurately set the location of the detecting electrode in relation to the rollers and in order to perform accurate ink detection. If the detecting electrode is not accurately set, there will occur such a problem as inaccurate ink detection. Since there exists a limited space for mounting the detecting electrode within a narrow printing drum of the printing apparatus, the setting of the ink detecting device is much restricted. US-A-3,747,084 describes a liquid level gauge for supervising the level of a liquid such as the level in an ink receptacle of a printing press. It comprises a probe which is driven to perform repetitive, pendulum, uniform motions and so arranged that it dips into the ink when the level thereof exceeds a predetermined height. Dipping of the probe into the ink and the resulting increased resistance thus experienced by the probe cause the probe to vary the repeat pattern of its motions. This variation is utilized via switch means controlled by the probe motions to produce an electrical pulse pattern used to stop the feeding of ink into the receptacle thereby effectively preventing over-filling of the ink receptacle. When the liquid level in the receptacle reaches a height causing braking of the pendulum motions, the repetition frequency of the pulses will drop below a required minimum speed and an ink feed pump will be stopped. The pump will automatically resume feeding ink whenever the liquid level therein sinks below the level at which the tip of the arm of the pendulum dips into the ink, as at that point the pendulum resumes its normal pattern of motions thereby restoring the normal pulse pattern generated by the pendulum. It is therefore an object of the present invention to provide a motor-type ink sensor which can be easily set within a narrow printing drum of a printing apparatus and accurately detect the presence or absence of ink regardless of mounting accuracy. The motor-type ink sensor of the present invention is an ink sensor for detecting ink by a printing means of the printing apparatus, and has an agitating part disposed in the position of an ink fountain formed in the printing means, a motor for rotating the agitating part, and a control section for detecting ink from the driving condition of the motor, and wherein the control section judges the quantity of ink by detecting the driving condition of the motor from the load current of the motor which is driven at a rated or lower voltage. The motor-type ink sensor of the present invention may be designed so that the control section outputs an "Empty" signal when the quantity of ink has been judged to be under a reference value, driving the ink supply section according to the "Empty" signal, and, optionally, wherein the control section outputs the "Empty" signal, driving the ink supply section only when an "Enable" signal to be outputted only when ink supply is needed has been entered into the control section. The motor-type ink sensor of the present invention may be provided with a restart signal generating circuit for restarting the motor from a stop, and, optionally, be of such a design that the restart signal generating circuit gives the motor a restart signal, which is stronger than the restart signal stated above, when the motor will not start if given a predetermined number of restart signals, and, further optionally, be of such a design that the restart signal generating circuit which gives the motor a stronger restart signal when the motor will not restart. According to the aforementioned constitution, the motor at a stop is restarted by the input of the restart signal when ink runs out, thereby starting the rotation of the agitating part. At this time little load current is flowing in the motor, from which the absence of ink will be detected. With the supply of ink the quantity of ink reserved becomes large until the agitating part contacts ink, thus easily stopping the motor being driven at a rated or less voltage. At this time a great load current is flowing in the motor, thereby detecting the presence of ink. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a sectional view of one embodiment of a mimeograph apparatus in which a motor-type ink sensor of the present invention is used; Fig. 2 is a perspective view showing the interior of a printing drum in the embodiment of the mimeograph apparatus; Fig. 3 is a sectional view showing the interior of the printing drum in the embodiment of the mimeograph apparatus; Fig. 4 gives front and right side views showing an agitating part of the motor-type ink sensor in the embodiment; Fig. 5 is a block diagram showing the constitution of the motor-type ink sensor and a control section in the embodiment; Fig. 6 is a timing chart showing an operation timing of the motor-type ink sensor and the control section thereof in the embodiment; Fig. 7 is a flow chart showing the operation of the embodiment; Fig. 8 is a sectional view showing another example of constitution of a squeegee device in the embodiment; Fig. 9 is a timing chart exemplifying a method of supplying a restart signal in the embodiment; Fig. 10 is a table showing a relationship between the temperature and viscosity of ink to be used on the squeegee roller in the embodiment; Fig. 11 is a table showing a relationship between the temperature and viscosity of ink to be used on a squeegee blade in the embodiment; and Fig. 12 is a sectional view showing a conventional electrostatic capacity type ink detecting device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Fig. 1 shows the internal construction of a mimeograph apparatus 1 in which a motor-type ink sensor of the first embodiment is mounted. The mimeograph apparatus 1 has an original image reading section 2 and a stencil preparing section 4 for forming a perforated image in a roll-type stencil paper 3 according to a data from the reading section 2. Adjacently to the stencil preparing section 4 there is provided a cylindrical printing drum 5 as a printing means which is wrapped with the perforated stencil paper 3 on the outer peripheral surface is driven to rotate. And inside the printing drum 5 are mounted an ink supply means, a liftable squeegee, etc. Furthermore, beneath the printing drum 5 are mounted a press roller 6 and a printing paper supply section 7, so that the printing paper 8 is fed in and the press roller 6 is moved up and down simultaneously with the rotation of the printing drum, thus performing mimeographing successively. A reference numeral 9 in the drawing refers to a stencil discharge box for holding a used stencil paper that has been stripped from the printing drum. Figs. 2 and 3 show the interior of the printing drum 5 of the mimeograph apparatus 1. A squeegee roller 10 is mounted on the inner peripheral surface of the printing drum 5 at the bottom thereof. The outer peripheral surface of the squeegee roller 10 is in contact with the inner peripheral surface of the printing drum 5. In Fig. 3 a doctor roller 11 is parallelly disposed at a slight spacing on the left side of the squeegee roller 10, in the printing drum 5 which rotates in the counterclockwise direction. In the vicinity of the squeegee roller 10 and the doctor roller 11 a driving rod 12 is rotatably mounted in parallel with the rollers 10 and 11. Also, a little above the right-hand side of the squeegee roller 10 is mounted an ink distributor 13 which communicates with the ink supply means. Ink supplied from the ink distributor 13 forms an ink fountain 50 between the squeegee roller 10 and the doctor roller 11, being agitated by the driving rod 12. Above the top of the squeegee roller 10 is mounted a sensor motor 21 of a motor-type ink sensor 20 with its rotating shaft directed toward the squeegee roller 10. On the forward end of the rotating shaft of the sensor motor 21 is installed an agitating part 22. This agitating part 22 is disposed on the right of the driving rod 12, that is, in a position corresponding to the right-hand end of the ink fountain 50. The agitating part 22 can be disposed in other position, that is, above the driving rod 12. The sensor motor 21 is connected to a control section 24. The control section 24 has a function to judge the presence and absence of ink by detecting the driving condition of the sensor motor 21 from the load current of the sensor motor 21 which is driven at a rated or lower voltage. The motor-type ink sensor 20, which will be described in detail later, has the agitating part 22 which is driven by the sensor motor 21, in the vicinity of the ink fountain 50, for the purpose of monitoring the load which the sensor motor 21 receives from ink in order to detect ink while comparing the load with a reference value. That is, the motor-type ink sensor 20 has such a constitution that when no ink is present, the sensor motor 21 turns, and when a specific amount of ink is present, ink holds on the agitating part 22 to thereby stop the sensor motor 21; and with the supply of a start signal to the sensor motor 21 at a specific time interval, the sensor motor 21 that has once stopped restarts operating. The agitating part 22 of the motor-type ink sensor 20, as shown in Fig. 4, comprises a center shaft 25 and a blade section 26. On the base end of the center shaft 25 the rotating shaft of the sensor motor 21 is mounted by pressing. The length of the center shaft 25 is set in order that a distance from the top end of the blade section 26 to the bottom surface of the sensor motor 21 will be around twice as large as the height of blade section 26. If the distance between the agitating part 22 and the sensor motor 21 is small, ink will attach between the agitating part 22 and the sensor motor 21, resulting in hard restart of the sensor motor 21. In the present embodiment, however, the agitating part is provided with a long center shaft 25 and ink attaches only on the agitating part 22; therefore a greater resistance than needed will not be applied to the rotation of the sensor motor 21 by the ink holding on the agitating part 22. The blade section 26 has two blades each having smooth surfaces with little irregularities. Therefore, there will not occur such a trouble that an unnecessary amount of ink attaches to, and is held on, the blade surface and between the blades, and accordingly the restart of the sensor motor 21 from a stop will not be interrupted. Since the center shaft 25 and the blade section 26 are formed of a light-weight resinous material, for example, polyacetal and ABS resin, which will not give an adverse effect to the rotation of the sensor motor 21, the sensor motor 21 being driven at a rated or lower voltage receives a great deal of load owing to the adhesion of ink, thus causing a current variation. Next, the circuit formation of the sensor motor 21 and the control section 2 in the motor-type ink sensor 20 will be explained by referring to Fig. 5. The sensor motor 21 is a miniature d.c. motor, which, in the present embodiment, is driven at a rated or lower voltage. The current flowing into the sensor motor 21 is amplified by an amplifier 30 through a waveform shaping circuit 31 after conversion to a voltage through a current-voltage conversion circuit, and then is inputted to a comparing section 32, where the voltage is compared with a reference voltage not shown which is applied to the comparing section 32. If the voltage of the sensor motor 21 is less than the reference voltage, an "Empty" signal will be outputted. That is, when no ink is present (or the remaining amount of ink is less than the reference value), the ink will not attach to the blade section 26 of the agitating part 22, and therefore the sensor motor 21 can be kept running at the rated or lower voltage; however, when ink supplied attaches to the blade section 26, the sensor motor 21 receives load and the load current rises. An increase in the voltage caused by the rise of the load is compared with the reference voltage by the comparing section 32, thereby detecting the occurrence of load caused by the adhesion of ink. The "Empty" signal is inputted into an AND circuit 33. To this AND circuit 33 an "Enable" signal is also inputted. The "Enable" signal is a signal which allows the start of ink supply. In the mimeograph apparatus 1, it is not necessarily permitted to supply ink at any time if little amount of ink remains, for example no ink supply is required during stencil preparation and during a stop of the apparatus. The "Enable" signal is produced and inputted to the AND circuit 33 so that when ink supply is needed, for example only when the printing drum 5 rotates to supply a printing paper 8 during printing, ink supply will be permitted. Where ink detection is not needed, for example when the printing drum 5 is not rotating, the sensor motor may be stopped. A drive signal is outputted only when both the "Empty" signal and the "Enable" signal have been entered into the AND circuit 33. As shown in Fig. 5, the drive signal is inputted into the driving section 34, which in turn drives a pump motor 35 to supply ink. The sensor motor 21, when once stopped by ink supplied, will remain stationary even when the ink is used out, resulting in a failure in detecting the absence of ink. Therefore, as shown in Fig. 5, the sensor motor 21 is designed such that a restart signal will be inputted at a specific cycle. In Fig. 5, a reference numeral 6 denotes a restart signal generating circuit, such as a multivibrator, which generates a short wave with a specific period. In the present embodiment, the multivibrator generates a short wave with a period of three seconds. A reference numeral 37 denotes a restart switching circuit which generates a pulse-type restart signal by catching the edge of rise or fall of the short wave from the restart signal generating circuit 36. In the present embodiment, the length of the restart signal is set at 250 msec. The restart signal produced from the restart switching circuit 37 is fed to a motor driving circuit 39, thus driving the sensor motor 21. When the restart signal is fed into the sensor motor, the voltage applied to the sensor motor 21 also increases. However, there will never occur such a misjudgment that, with the application of the pulse-type high voltage to the sensor motor 21, the sensor motor 21 is loaded and decides as if ink were present in the printing drum notwithstanding the absence of ink. It is because the pulse-type voltage of the sensor motor 21 generated by the restart signal is changed in waveform by means of the waveform shaping circuit 31 and becomes less than the reference voltage at the comparing section 32. In the motor-type ink sensor of the aforesaid constitution, when ink to be supplied is not present in an ink reservoir, ink supply will fail if the pump motor 35 is driven in an attempt to supply the ink when required as a result of ink detection in the printing drum 5. Therefore, the sensor motor 21 keeps on rotating. When the "Empty" signal has been successively outputted for at least an arbitrarily set specific period of time, the absence of ink may be decided and displayed on a control panel not shown of the mimeograph apparatus 5. Next, the operation timing of the sensor motor 21 and the control section 24 in the motor-type ink sensor 20 will be explained with reference to Fig. 6, in which explanation it is assumed that an "Enable" signal has been outputted. In (1) when a restart signal is inputted into the sensor motor 21 in such a condition that the quantity of ink is under a specified quantity ("Empty" level in the drawing), the sensor motor 21 starts rotation shown in (2). With the rotation of the sensor motor 21 as shown in (2), the Empty signal is outputted at the time of start of rotation, and the pump motor 35 is turned on to start supplying the ink. When the quantity of ink exceeds a specified quantity ("Full" level in the drawing) as shown in (3), the blade section 26 of the agitating part 22 will be loaded with ink, stopping the sensor motor 21, whereby no Empty signal will be outputted; therefore, as shown in (4), the pump motor 35 also will be stopped. The restart signal is continuously fed to the sensor motor 21 with a specific period also while the specified quantity of ink is present. The quantity of ink will soon decrease again to the specified quantity or less as shown in (5). The sensor motor 21 restarts operation as shown in (6) according to the first restart signal after the decrease of the ink quantity to the specified quantity or less. Then, with the rotation of the sensor motor 21, the pump motor 35 is driven as shown in (7). According to the operation timing explained above, there can be obtained an operation sequence of the mimeograph apparatus 1 as shown in Fig. 7. That is, at Step 1, when the whole body of the mimeograph apparatus 1 is turned on, the sensor motor 21 as shown at Step 2 will start. Then, as shown at Step 3, the pump motor 35 will be driven to start the supply of ink as shown at Step 4 only when the sensor motor 21 is rotating (an Empty signal is present) and ink supply is permitted (an "Enable" signal is present). At Step 3, the pump motor 35 is stopped to stop ink supply as shown at Step 5 when the sensor motor 21 is not rotating (the Empty signal is not present) and ink supply is not permitted (the "Enable" signal is not present). The embodiment explained above pertains to the mimeograph apparatus 1 having the squeegee roller 10 in the printing drum 5 as shown in Fig. 3; the constitution of the squeegee device in the printing drum 5, however, may be one as shown in Fig. 8. The squeegee device shown in Fig. 8 is of such a construction that an elastic plate-like squeegee blade 40 is moved up and down, by means of a lift driving mechanism not shown, into contact with the inner peripheral surface of the printing drum 5 to thereby force ink out of the printing drum. In relation to this squeegee blade 40, the ink distributor 13 is disposed adjacent to the advance side in the direction of rotation of the printing drum 5 indicated by an arrow. The ink supplied from the ink distributor 13 gathers between the squeegee blade 40 and the inner peripheral surface of the printing drum 5. In this ink fountain 50 is provided an agitating rod 41 in parallel with the longitudinal direction of the squeegee blade 40, for agitating the ink in the fountain 50. With respect to the constitution of the squeegee device stated above, the sensor motor 21 of the motor-type ink sensor 20 is disposed in the vicinity of the edge of the squeegee blade 40 near the distributor 13 as shown in Fig. 8. Here, the agitating part 22 is disposed to the right in the drawing of the agitating rod 41, that is, in a position corresponding to the right-hand end of the ink fountain 50 apart from the contact section between the squeegee blade 40 and the printing drum 5. Next, the supply of the restart signal to the sensor motor 21 will be explained. The sensor motor 21 is for detecting load according to the viscosity of ink; the ink viscosity differs with the type of the ink and environmental temperatures. Therefore, when the ink holds between the agitating part 22 and the sensor motor 21, it is necessary to give a restart signal, for restarting the sensor motor 21 that has once stopped, in accordance with the viscosity of the ink remaining between the agitating part 22 and the sensor motor 21, and to restart exactly in such a state that there remains no ink in the ink fountain. For example, if the sensor motor 21 will not restart when supplied with a common restart signal, it is conceivable that the ink viscosity is greater than an assumed value. In this case, as shown for example in Fig. 9(a), it is advised to give a restart signal SG2 of greater strength after repeating the restart signal SG1 several times. To increase the strength of the signal, the length of time to apply the signal may be increased or the voltage value or current value may be increased. Also both the time and voltage value (or the current value) may be increased. In case the sensor motor 21 will not restart even when supplied with a restart signal SG2 of greater strength, it is sufficient to supply a stronger restart signal SG3 as shown for example in Fig. 9 (b). Also, when the sensor motor 21 is restarted by giving a restart signal SG2 of greater strength than the common restart signal SG1, the common restart signal SG1 is then supplied to judge if the sensor motor 21 operates or not. When the sensor motor 21 will not turn if supplied with the restart signal SG2, a greater restart signal may be supplied to judge if or not the sensor motor 21 operates as shown in Fig. 9 (b). Furthermore, as described above, the agitating part 22 driven by the sensor motor 21 of the present embodiment is so constituted that the ink will not unnecessarily adhere thereon, but a stronger signal may be given to the sensor motor 21 for the purpose of removing the ink off from the agitating part 22 once in a while. Fig. 10 shows the ink viscosity by the temperature of ink applied to the squeegee roller 10. Fig. 11 shows the ink viscosity by the temperature of ink applied to the squeegee blade 40. Since it is conceivable that the greater the ink viscosity, the stronger the restart signal is required; therefore, the ink sensor may be so constituted that the strength of the aforesaid restart signal will be automatically adjustable in accordance with data on the ink viscosity stated above. That is, the ink sensor may be provided with a temperature measuring means, a control means operating on the data of ink viscosity relative to temperature, and a means for adjusting a pulse width and generating interval of the restart signal, to thereby produce the restart signal of proper pulse width and at a proper generating interval corresponding to an actual ink viscosity. According to the motor-type ink sensor 20 of the present embodiment, the following effect can be obtained as explained above. First, the sensor motor 21 is driven with a rated or lower voltage and therefore is usable for a longer life as compared with that used at a rating. The arrangement of the sensor motor 21 for detecting the presence or absence of ink is restricted less than the prior art electrostatic capacity type ink detecting device which is restricted largely with the arrangement of the detecting electrode. The control section 24 can be disposed outside of the printing drum 5. In the embodiment heretofore explained, the presence or absence of the ink is detected by the rotation or stop of rotation of the sensor motor 21. And therefore it is possible to gradually detect the quantity of ink by gradually judging the load current of the sensor motor 21. According to the motor-type ink sensor of the present invention, the ink is detected from the driving condition of the motor equipped with the agitating part disposed in the vicinity of the ink fountain; and therefore it is possible to easily set the ink sensor inside of a narrow printing drum of a printing apparatus, and moreover can accurately detect the presence or absence of ink regardless of a mounting accuracy.

Claims: An ink sensor for detecting ink in a printing means of a printing apparatus (1), said ink sensor comprising: an agitating part (22) disposed in the position of an ink fountain (50) formed in said printing means, a motor (21) for turning said agitating part (22), and a control section (24) for detecting ink from the driving condition of said motor (21), and wherein said control section(24) judges the quantity of ink by detecting the driving condition of said motor (21) from the load current of said motor (21) which is driven at a rated or lower voltage. An ink sensor according to claim 1, wherein said control section (24) outputs an "Empty" signal when it has judged that the ink quantity is under a reference value, thereby driving an ink supply section. An ink sensor according to claim 2, wherein said control section (24) outputs said "Empty" signal, and drives said ink supply section only when an "Enable" signal outputted only when the supply of ink is required is inputted into said control section (24). An ink sensor according to claim 1, further comprising a restart signal generating circuit (6) for supplying to said motor (21) a restart signal (SG1) for restarting said motor (21) from a stop. An ink sensor according to claim 4, wherein said restart signal generating circuit (6) gives said motor (21) a stronger restart signal (SG2) than said restart signal (SG1) when said motor (21) fails restarting even after supplying a predetermined number of restart signals. An ink sensor according to claim 5, wherein said restart signal generating circuit (6) gives said motor a stronger restart signal (SG3) when said motor (21) fails restarting.

Inventors: HASEGAWA TAKANORI, SHOJI HIDEO, HASEGAWA, TAKANORI, SHOJI, HIDEO, HASEGAWA, TAKANORI, C/O RISO KAGAKU CORPORATION, SHOJI, HIDEO, C/O RISO KAGAKU CORPORATION
Applicants: RISO KAGAKU CORP, RISO KAGAKU CORPORATION
Application year: 1994
Main classification: B41F31
IPC codes: G01V9, G01F23, B41F31, B41L13